This invention relates to an eye-contact lens, consisting of mainly concentric parts, having mutually different focal distances.
Such types of lenses are generally well known. For instance lenses are known for correcting the course of light rays to the eye in cases of presbyopia, having at their convex outer surface a brim-part, ground for correcting rays in case of myopia. The surface of the brim-part, being part of the outer surface of the lens then has a smaller radius than the part of the outer surface it surrounds, the central part, while the thickness of the brim-part gradually decreases towards the edge of the lens. Also other eye-contact lenses are known for correcting the course of rays in case of myopia, provided with a bowl-shaped recess in the concave inner surface for correction of presbyopia.
These known bifocal lenses however have their disadvantages. More particularly, a sharp image is only obtained for two distance-intervals, whereas the transition from far-sight to short-sight is a discontinuous one and is considered an inconvenience.
Some have tried to overcome the said disadvantages of designing multi-focal lenses, where the power of the lens changes gradually from the middle part of the lens towards the edge thereof. This however entails a disadvantage, in that because of the changing power, an optimally sharp image on the retina is never obtained.
Due to increasing demand for bifocal contact lenses and the disappointing results with current concepts such as the mentioned crescent and concentrical shapes, a new concept, the bi-trifocal contact lens was developed in our office.
The eye-contact lens according to the present invention avoids the disadvantages of the bifocal lens and of the multi-focal lenses. To that end, the eye-contact lens according to the present invention consists of at least three parts:
a central part, confined by the brims of a bowl-shaped recess at the inside/concave side of the lens; PA1 a brim-part around the periphery of the lens, having at the outside or the convex side of the lens, a surface with a radius which is smaller than that of the surface of the inner part and having a thickness which from the inside to the outside decreases gradually; and PA1 a part, situated between the central part and the brim-part, the surfaces of which, both at the inside and at the outside of the lens, connect the surfaces of the central part and the brim-part.
The brim-part and the middle part in most of these lenses are concentric with respect to the central part.
Thus it is possible and it is an object to provide one lens, to correct both for presbyopia and for myopia. Therefore the part-in-between obtains good image-forming characteristics for the distance interval between `close by` and `far off`. A further positive contribution is that it makes the transition from long distance to short distance, a gradual one thus avoiding the earlier mentioned inconvenience for the user.